1. Field of the Invention
The present invention relates to a novel rayon fiber which possesses characteristics similar to those of a viscose rayon fiber as to be suitable for use in clothes in addition to being produced at economical cost. Also, the present invention is concerned with a method for producing such a rayon fiber. As used herein, the term xe2x80x9crayon fiberxe2x80x9d is defined as a fiber made of a polymer of xcex2-D-glucopyranose (hereinafter referred to as xe2x80x9ccellulosexe2x80x9d) in which not more than 15% of the hydroxyl groups have been substituted.
2. Description of the Prior Art
Rayon fibers are used for high quality clothes by virtue of their characteristic gloss, specific gravity, and good sense to the touch. Usually, viscose rayon (hereinafter referred to as xe2x80x9crayonxe2x80x9d) fibers are made by spinning, in an aqueous solution of sulfuric acid and zinc sulfate, an aqueous sodium cellulose xanthate solution which is prepared by dissolving cellulose in a caustic soda solution using carbon disulfide (CS2). However, to produce viscose rayon fibers is very difficult. For example, during the production of viscose rayon fibers, highly toxic materials, such as carbon disulfide, are generated. In addition, since a dyeing difference is apt to occur between an inner and an outer layer even in the same pirn, fiber products of uniform color are very difficult to produce.
Lyocell fibers, which are spun from a solution of cellulose in N-methylmorpholine-N-oxide, have not been processed into textile products owing to their excessive stiffness and expensive cost until a recent success of enzymatic processing. Fortisan, a high tenacity viscose rayon manufactured by Celanese, is prepared by drawing cellulose acetate and saponifying the drawn cellulose acetate with alkali. With a tenacity as high as 7 gf/de and an elongation as low as 8%, Fortisan can find numerous applications in the industrial fiber industry, including tire cords, conveyor belts, fire hoses and so on.
Methods for preparing rayon from cellulose acetate can be found in Robert, W. Work, TEXTILE Research Journal, Vol. XIX, No. 7, pp 381-393, July, 1949, which is responsible for the production of Forthisan and to U.S. Pat. No. 2,053,766 which discloses a high tenacity rayon yarn (tenacity 2.5 gf/de or higher). According to the references, spun acetate fibers are drawn and saponified with alkali to produce rayon fibers having a cellulose II crystalline structure. Their high tenacity and poor elongation restrict the rayon fibers to industrial uses. Even so, they are not produced owing to high cost.
Therefore, it is an object of the present invention to provide a rayon fiber which is similar in characteristics to a viscose rayon fiber, suitable for use in clothes and producible at economical cost.
It is another object of the present invention to provide a method for producing such a rayon fiber with ease.
It is a further object of the present invention to provide cloth products using such a rayon fiber, including woven, knitted fabric, and non-woven fabrics.
In accordance with a first embodiment of the present invention, there is provided a rayon fiber, possessing a composite crystalline structure of cellulose II and IV, which is prepared by saponifying at least 75% of the total acetyl groups of a cellulose acetate fiber with a degree of substitution of at least 2.0 into hydroxyl groups.
In accordance with a second embodiment of the present invention, there is provided a method for preparing a rayon fiber, comprising the step of treating a cellulose acetate fiber with a strong alkali alone or with a strong and a weak alkali in the same bath or different baths to saponify at least 75% of the total acetyl groups of the cellulose acetate fiber into hydroxyl groups, said cellulose acetate fiber having a degree of substitution of 2.0 or higher, whereby the rayon fiber has a composite crystalline structure of cellulose II and IV.
In accordance with a third embodiment of the present invention, there is provided a method for preparing a rayon fiber, comprising the step of treating a fiber material comprising cellulose acetate fibers alone or in combination with other fibers with a strong alkali alone or with a strong and a weak alkali in the same bath or different baths to saponify at least 75% of the total acetyl groups of the cellulose acetate fibers into hydroxyl groups, said fiber material being selected from a woven fabric, knitted fabric and a non-woven fabric, which are made by weaving, knitting or niddle punching cellulose acetate fibers alone or in combination with other fibers, said cellulose acetate fibers having a degree of substitution of 2.0 or higher, whereby the rayon fiber has a composite crystalline structure of cellulose II and IV.
In accordance with a fourth embodiment of the present invention, there is provided a method for producing a rayon film, comprising the step of treating a cellulose acetate film with a strong alkali alone or with a strong and a weak alkali in the same bath or different baths to saponify at least 75% of the total acetyl groups of the cellulose acetate film into hydroxyl groups, said cellulose acetate film having a degree of substitution of 2.0 or higher, whereby the rayon film has a composite crystalline structure of cellulose II and IV.
In accordance with a fifth embodiment of the present invention, there is provided a rayon fiber product, comprising a rayon fiber which possesses a composite crystalline structure of cellulose II and IV and is prepared by saponifying at least 75% of the total acetyl groups of a cellulose acetate fiber with a degree of substitution of 2.0 or higher into hydroxyl groups.
In accordance with a sixth embodiment of the present invention, there is provided a rayon film, which is prepared from a cellulose acetate film with a degree of substitution of 2.0 or higher by saponifying at least 75% of the total acetyl groups of the film into hydroxyl groups and possesses a composite crystalline structure of cellulose II and IV.